The present invention relates to an apparatus and method for cleaning the interior of a heat exchanger by controlling the flow of separate fluids flowing through separate fluid conduits of the heat exchanger.
One of the known methods of cleaning a heat pump is an acid cleaning process. One gallon of muriatic acid is mixed with three gallons of water to create a 25% muriatic acid solution in a five gallon plastic bucket. The water inlet and outlet hoses are disconnected from the heat pump. An acid pump is positioned within the five gallon plastic bucket with an outlet hose connected to the outlet of the heat pump, while another hose is connected to the inlet of the heat pump for discharging the 25% muriatic acid solution back into the five gallon plastic bucket while being recirculated by the acid pump. The pump is selected with components to tolerate a 25% muriatic acid solution. The 25% muriatic acid solution is circulated through the heat pump in through the outlet port and out through the inlet port for 20-30 minutes. The heat pump is then flushed with pure water. The water inlet and outlet hoses are then reconnected to the heat pump. This process requires extreme caution when handling muriatic acid. The operator is required to wear eye protection and protective gloves, and it is recommended to only be performed by a trained technician.
Ground water heat pump installations can require cleaning on a regular basis due to poor quality ground water. Water treatment normally is not an option due to the large amounts of water used with ground water heat pump installations as opposed to a closed loop system. The normal course of cleaning is to require acid cleaning of the water coil or heat recovery unit. If scaling of the coil is suspected, the coil can be cleaned with a solution of phosphoric acid (food grade acid).
The instructions typically indicate that the manufacturer""s directions for mixing, use, etc. should be followed. The acid solution can be introduced into the heat pump coil through a hose bib. The isolation valves are closed to prevent contamination of the rest of the system by the acid. The acid is pumped from a bucket into the hose bib and returned to the bucket through the other hose bib. The standard instructions typically indicate that the manufacturer""s directions for the product used should be consulted to determine how long the solution is to be circulated, but is usually circulated for a period of several hours.
The present invention provides an apparatus for removing deposits that accumulate on an interior surface of a heat exchanger. The apparatus removes deposits by controlling the flow of the separate fluids that concurrently pass through the heat exchanger. The heat exchanger includes a heat transfer wall that separates the flow of the two fluids. The flows of the respective fluids are controlled by control means. The cleaning cycle control system, through the control means, engages a heating cycle so that a first fluid draws heat from the second fluid through the heat transfer wall. The second fluid begins to freeze along the heat transfer wall. The deposits located on the heat transfer wall, on the side of the second fluid, also begin to freeze. After the freezing process has progressed for a period of time, the cleaning cycle control system, through the control means, reverses the flow of the first fluid so that heat is directed toward the second fluid. Frozen deposits positioned on the wall begin to thaw. The thawing process causes the deposits to separate from the heat transfer wall. The flow of the second fluid carries the deposits away from the heat exchanger. The present invention can also include a solenoid water valve positioned within the second fluid conduit. When the cooling cycle is actuated to thaw the frozen deposits, the solenoid valve is reactivated. The present invention also provides means for disengaging a freeze switch or pressure switch to allow the heat transfer wall to at least partially freeze. Disengaging the switch allows the cleaning cycle control system, through the control means, to operate without interruption by the switch. The present invention also provides means for automatically engaging the cleaning cycle control system, through the control means, after the heat exchanger has operated for a predetermined period of time.
The present invention provides a method for cleaning a heat transfer wall in a heat exchanger. A heating cycle is engaged to draw heat from a fluid in the heat exchanger. The heat is drawn from the fluid through a heat transfer wall. Fluid immediately adjacent to the heat transfer wall and deposits on the heat transfer wall at least partially freeze. The heating cycle is reversed and heat is absorbed by the fluid so that the fluid and deposits adjacent to the heat transfer wall thaw and separate from the heat transfer wall. The present invention also provides the step of shutting off the flow of fluid through the heat exchanger while the freezing process is proceeding. Also, the present invention provides the step of disengaging a freeze switch operably associated with the heat exchanger to prevent the heating cycle from shutting down before a predetermined period of time has transpired. In addition, the present invention also provides the step of automatically engaging the cleaning process for the heat exchanger after the heat exchanger has operated for a predetermined period of time.